// Problem: 
// Contest: 
// URL: 
// Memory Limit: 
// Time Limit: 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
int L,n,k;
vector<int> v;
bool f(int x)
{
	int c=k,sit=0;
	for(int i=2;i<=n;i++)
	{
		if(c<0)break;
		if(v[i]-sit<=x)sit=v[i];
		else
		{
			sit=sit+x;
			i--;c--;
		}
	}
	if(c>=0)return true;
	else return false;
}
signed main()
{
	cin>>L>>n>>k;
	v=vector<int> (n+1);
	for(int i=1;i<=n;i++)
	{
		cin>>v[i];
	}
	sort(v.begin()+1,v.end());
	int l=1,r=L;
	while(l<r)
	{
		int mid=(r-l)/2+l;
		if(f(mid))r=mid;
		else l=mid+1;
	}
	cout<<l;
	return 0;
}
